Pelton Wheel Questions and Answers

Answer: A

For a Pelton wheel the hydraulic efficiency is maximum when the bucket speed is half the jet speed, and then

where \(\phi\) is the vane angle at the outlet. For a smooth bucket that turns the jet right round (\(\phi = 0\)) this gives 100 percent. The options with sin phi or with cos phi alone (over 2) do not have this property: the second would give an efficiency of 50 percent when phi is zero, and the third and fourth would give 50 percent and zero.

Answer: A

Pelton turbines are tangential flow turbines.

In a Pelton wheel the water jet strikes the buckets along the tangent to the runner's circumference. It is an impulse turbine used for high heads and low discharge.

The Francis turbine is a radial (inward) or mixed flow reaction turbine, and the Kaplan and propeller turbines are axial flow.

Answer: B

The Pelton turbine is a high head and low mass flow rate turbine.

The Pelton wheel is an impulse turbine. A nozzle turns the whole available head into a high-velocity jet that strikes buckets on the runner rim, at atmospheric pressure. It suits heads of several hundred metres and above, with relatively small discharges, as in mountain hydro stations, and it has a low specific speed.

Low head and high flow is the domain of the Kaplan and propeller turbines, and medium head and medium flow that of the Francis turbine. High head with high flow is not a regime the Pelton wheel is designed for, because a large discharge needs several jets or a larger, slower runner.